Depending on the size and design of an aircraft, engine start systems differ from each other in their design. Smaller engines, for example turboprop engines for regional aircraft, turboshaft engines for helicopters, or piston engines for smaller aircraft are presently preferably started electrically, wherein the electrical power is taken from a battery. Medium-sized and large aircraft that comprise turbojet engines predominantly use a pneumatic system for starting the main engines. In this process, compressed outside air is fed to a starter turbine which consequently rotates, thus producing a mechanical shaft output that by way of a gear arrangement is transmitted to a main shaft of the engine to be started. This process is maintained until after ignition in combustion chambers the engine independently accelerates to operating speed. The pneumatic energy required for starting is provided by bleed air, for example from an auxiliary gas turbine, from some other already started engine, or from external ground equipment, and is fed to the starter turbine by way of a bleed-air distribution system. Before and after engine start the bleed air is predominantly made available to air conditioning packs of an air conditioning system of the aircraft.
In aircraft which provide for increased utilization of electrical energy for operating systems, and thus provide less or no utilization of bleed air when compared to aircraft that are presently in widespread use, starting the engine is typically achieved by means of electrical energy. For this purpose either electrical starter motors or alternatively combined starter/generators are provided on the main engine. In this setup, too, the shaft output is applied, by way of a gear arrangement with a particular transmission ratio, to an engine main shaft. The electrical energy is provided by means of generators of the auxiliary gas turbine, by means of another engine already in operation, or by means of external ground equipment, with the electrical energy being conveyed to the electrical starter by way of the electrical network of the aircraft.
EP 1 817 231 A2 and US 20080001026 A1 describe a supply system for an aircraft, in which engine start takes place by means of electrical energy provided by a fuel cell.
In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.